1. Field of the Invention
The present invention relates to a rolling bearing unit suitable for use in a belt transmission system and a belt drive system disposed around various machine motors or a vehicle engine (for example, an alternator, an intermediate pulley, an electromagnetic clutch, a compressor and a water pump, etc.).
2. Description of the Related Art
In a rolling bearing used in the components of a rotary shaft in the vehicle or rotary shafts in various machine motors, due to the occurrence of the static electricity or the leak of the current from the electric circuit, the potential difference occurs between the inner and outer rings and therefore a current flows between them through the rolling bodies. In this case, as the contact between the rolling bodies and the inner and outer rings is the point contact or the line contact, there occurs electric discharge at the point contact or in the line contact due to large contact resistance. Accordingly, the electrolytic corrosion is occurred on the surfaces of the rolling bodies and on the raceway surfaces of the outer and inner rings, which lowers the life of the rolling bearing.
Further, around the vehicle engine, rotation is transmitted from a crankshaft through a drive pulley and a belt to a passive pulley mounted on the leading end portion of auxiliary machinery such as an alternator, an electromagnetic clutch or a compressor. In case where the drive pulley is made of iron, due to friction between the pulley, to which the high-speed rotation of the crankshaft of the engine is transmitted, and the frictional contact surface of the belt, there is generated static electricity of several hundreds volts to 5000 volts although it is discharged in part to the atmosphere. A current, which occurs due to such static electricity, for example, as disclosed in Japanese Patent Unexamined Publication No. Hei. 4-160225, flows into a rolling bearing existing close to the pulley and thus, due to the electrolytic reaction of water contained in the lubricating grease of the rolling bearing, there is generated hydrogen. This raises a problem that such hydrogen enters the interior portion of the rolling surface of the bearing, which results in the early exfoliation thereof.
In related art, as a technology for solving such problem, for example, there is known an energizing bearing which is disclosed in the registered Japanese Utility Model No. 2540952. In this bearing, there is interposed a spiral-shaped spring between the end portion of the inner peripheral surface of an outer ring and the end portion of the outer peripheral surface of an inner ring that is opposed to the end portion of the inner peripheral surface of the outer ring. On one end side of the spring, there is formed an inner ring side sliding contact portion which can be slidingly contacted with the inner ring outer peripheral surface end portion. On the other end side of the spring, there is formed an outer ring side sliding contact portion which can be slidingly contacted with the outer ring inner peripheral surface end portion. The leading end portion of the outer ring side sliding contact portion is extended substantially up to the same position of the inner ring side sliding contact portion in the peripheral direction, thereby being able to prevent a discharge phenomenon which otherwise could occur between the raceways of the rolling bearing and rolling bodies.
The energizing bearing disclosed in the above-cited registered Japanese Utility Model No. 2540952 interposes the spiral-shaped spring between the rolling bodies and inner and outer rings to thereby eliminate a potential difference between them in order to be able to prevent the discharge phenomenon from occurring between the raceways of the rolling bearing and rolling bodies. However, in actual use, there is present lubricating oil between the inner ring and rolling bodies as well as between the outer ring and rolling bodies and thus there exists a clearance of several microns between them; and, therefore, the existence of a potential difference of several volts has been confirmed between them.
On the other hand, in Japanese Patent Unexamined Publication No. Hei. 11-117758, there is disclosed a member for engine electrically mounting auxiliary machinery which can prevent static electricity from flowing to the bearing side to thereby prevent the early exfoliation of the bearing due to the electrolytically produced hydrogen. However, in this structure, since an electrically insulated part formed of synthetic resin having low thermal strength is used in the drive pulley thereof, the strength of the drive pulley is not sufficient.
In view of the above, the present invention aims at eliminating the above-mentioned drawbacks found in the rolling bearing units in the related art. Accordingly, it is an object of the invention to provide a rolling bearing unit which removes static electricity occurring due to the rotation friction of a drive unit in front of the rolling bearing to thereby be able to prevent the early exfoliation of the rolling bearing.
In attaining the above object, according to a first object of the invention, there is provided a rolling bearing unit which a rolling bearing having an inner ring and an outer ring, one of the inner and outer rings supported by a support member, the other of the inner and outer rings supporting a rotary member rotatably, a drive unit for driving and rotating the rotary member, and a diselectrification member disposed in front of the rolling bearing that is disposed closest to the drive unit in an axial direction of the rotary member, for removing static electricity to be generated form the drive unit.
Here, the drive unit can comprises a pulley mounted on the rotary member and a belt for driving the pulley. The diselectrification member can comprise a contact type diselectrification device interposed between the above pulley and ground.
Also, the rolling bearing unit can be applied to the vehicle alternator.
In the rolling bearing unit according to the invention, static electricity to be generated due to rotational friction between the pulley and drive belt forming the drive unit is removed by the contact type diselectrification member interposed between the pulley and ground to thereby control a potential difference between the rotating and fixed rings of the rolling bearing down to 1 V or less so as to be able to control the electrolytic reaction of water contained in the grease of the bearing and thus prevent generation of hydrogen ions. Thus, the early exfoliation of the bearing can be prevented and thus the life of the bearing can be enhanced.